Research indicates the MP3 player headphones, not the player itself, poses a health risk to some owners

If you listen to an MP3 player and have a heart pacemaker, you could be at risk of complications, medical researchers warn.

But unlike previously thought, the MP3 player is not the culprit -- the headphones plugged into the MP3 player pose a risk. Earlier in 2008, the U.S. Food and Drug Administration (FDA) officially concluded that MP3 players are safe to use regardless of their location.

Research presented during the American Heart Association conference indicates that some headphones commonly used by MP3 player owners can interfere with pacemakers or implanted defibrillators -- even if they're not being used and are disconnected.

Researchers led by Dr. William Maisel at the Medical Device Safety Institute at Beth Israel Medical Center in Boston tested eight different models of headphones and ear buds that were connected to Apple iPod MP3 players. During the study with 60 patients, 30 percent of subjects with defibrillators and 15 percent of subjects with pacemakers suffered interference due to their headphones.

"For patients with pacemakers, exposure to the headphones can force the device to deliver signals to the heart, causing it to beat without regard to the patients' underlying heart rhythm," Dr. Maisel said in a press statement. "Exposure of a defibrillator to the headphones can temporarily deactivate the defibrillator."

A strong magnetic substance inside some popular MP3 headphones mistakenly interrupt a pacemaker's beat or deactivate the defibrillator.

If placed around one inch from a device, there was interference one-fourth of the time -- in 10 patients out of 33 who had defibrillators and four of 27 overall patients with pacemakers. One pacemaker unexpectedly reset itself during the trials.

Sixty patients took part in the study.

Dr. Maisel said people shouldn't "overreact" to the research, but still advised patients with pacemakers or defibrillators to keep headphones at least 3 centimeters away from the implanted devices. Furthermore, headphones should not be placed in a breast pocket or dangle over their chest.

"We can't expect users to use common sense. That would eliminate the need for all sorts of legislation, committees, oversight and lawyers." -- Christopher Jennings